In this regard, it is known, for example from JP 5941878 B2, how to channel the exhaust gas through numerous exhaust gas pipes, which are received in a housing, so that a flow can be generated with a liquid coolant, for example, such as water/glycol, between housing and the exhaust gas pipes, or between the exhaust gas pipes. However, in this case the cooler is heated, especially at the gas inlet side, which means that it has a much higher temperature here than in the further stretch. This results in an inhomogeneous temperature distribution in the material of the cooler and thus in stresses. In particular, temperature changes of the gas as well as the coolant such as occur on account of the nonstationary operating behavior of the internal combustion engine (e.g., cold starting, changing load, AGR rate, etc.) result in further inhomogeneities in the temperature distribution, given different material thicknesses and thus different temperature change rates, which result in the aforementioned stresses.
In the region of the gas inlet, such inhomogeneities occur in an especially critical form, since on the one hand the thin front edges of the exhaust gas pipes encounter the uncooled hot exhaust gas mass flow and can only give off the introduced heat slowly to the cooling water on account of their thin walls. On the other hand, the exhaust gas pipes here are usually joined at the sides to a housing, which has a much greater wall thickness and whose temperature therefore changes with greater inertia, or the housing walls are not directly exposed to the hot exhaust gas mass flow. In many applications, a thick-walled flange is situated outside the housing, which further intensifies the situation. The heated exhaust gas pipes expand in the inlet region, and since the temperature of the housing and/or the flange has not yet changed enough to result in a similar expansion, this differential expansion results in stresses.
The stresses result in a plastic deformation in the thinner component, the front edges of the exhaust gas pipe, which become compressed and/or form corrugations. Upon cooldown, either the relatively thin sheet metal cools down more quickly, or all the mentioned components cool down at the same time, but the compressed sheet metal must return to its starting position and expand, which creates tensile stresses in the front edge of the exhaust gas pipe. This alternating loading and plastic deformation results in failure of the material of the exhaust gas pipe. In this regard, one must also consider the fact that an exhaust gas cooler must withstand the described alternating loading for several 100,000 times in the course of its lifetime.